Expanded polystyrene (“foam”) coolers are inexpensive, lightweight, waterproof, and provide good insulation for the contents. They are popular with consumers for cooling food and beverages over short periods; such as day trips. However, these inexpensive foam coolers generally have a loose fitting lid, held in place by friction. The brittle nature of the foam material prevents using a tight friction fit for the lid, as that would likely cause breakage at the contact points between the lid and the cooler body. As a result, when a cooler is turned upside down, the lid almost always falls off, especially if the cooler has relatively heavy liquid contents—such as food, water, ice or other beverages. Moreover, the foam is so light, that even a breeze (common when coolers are used outside and particularly at the beach) or quick movement of the cooler (as takes place during transport) can cause the lid to dislodge or come flying off.
Use of conventional metal or hard plastic hinges or locking mechanisms is often not practical with foam, due to its brittle nature. It cannot take and/or keep screws or rivets in place in normal use. Some designs of external (non-molded) locking mechanisms for coolers are known, but they add cost to a locking mechanism which can be molded.